VPN enrollment protocol gateway

ABSTRACT

A virtual private network (VPN) enrollment protocol gateway is described herein. The protocol gateway is implemented as a registration authority that operates as an intermediary between routers and a certificate authority, allowing routers operating in accordance with one protocol to obtain and maintain certificates for a VPN from a certificate authority operating in accordance with another protocol. In accordance with one aspect, the gateway protocol supports various requests from the router, including router enrollment requests, get certificate revocation list request, get certificate requests, get certificate authority certificate requests, and password requests.

RELATED APPLICATIONS

[0001] This is a division of application Ser. No. 09/548,257, filed Apr.12, 2000, entitled “VPN Enrollment Protocol Gateway”.

TECHNICAL FIELD

[0002] This invention relates to secure communications, and moreparticularly to a protocol gateway allowing routers operating inaccordance with one protocol to obtain and maintain certificates for avirtual private network (VPN) from a certificate authority operating inaccordance with another protocol.

BACKGROUND OF THE INVENTION

[0003] Computer technology is continually advancing, resulting incontinually evolving uses for computers. One such use is communicatingwith other computers over a network, such as the Internet, to obtain orexchange information, purchase or sell goods or services, etc. Oneparticular type of communication that can be established is referred toas a “virtual private network” or “VPN”. In a VPN, portions of a network(such as the Internet) are used to establish secure communications fromone computer to another via multiple different routers in the network.The VPN allows users to use the larger network (e.g., the Internet) toconnect to another computer as if they were part of a dedicated securenetwork.

[0004] In order to operate as part of a VPN, a router enrolls for a VPNcertificate via a certificate authority (CA). This VPN certificate isthen provided to other routers that are part of the VPN and is used toauthenticate the router and may also be used to securely communicatewith the other routers. However, different protocols for enrolling forVPN certificates have arisen, many of which are incompatible with oneanother. For example, many routers available from Cisco Systems, Inc. ofSan Jose, Calif. use a proprietary protocol called Simple CertificateEnrollment Protocol (SCEP) for obtaining VPN certificates, while manycertificate authorities available from Microsoft Corporation of Redmond,Wash. use an incompatible enrollment protocol based on Public-KeyCryptography Standard (PKCS) #10 and PKCS #7. Thus, a router using SCEPwould not be able to enroll for a VPN certificate from a CA using PKCS#10 and PKCS #7.

[0005] Additionally, many routers and CAs are already manufactured andin use that operate based on such incompatible protocols. Therefore,re-designing such routers or CAs to be compatible with one another wouldrequire the replacement of many such pre-existing devices. Thus, itwould be beneficial to provide a solution that allows routers and CAs(including pre-existing routers and CAs) operating based on incompatibleprotocols to communicate with one another for VPN certificateenrollment.

[0006] The VPN enrollment protocol gateway described below addressesthese and other disadvantages.

SUMMARY OF THE INVENTION

[0007] A virtual private network (VPN) enrollment protocol gateway isdescribed herein. The protocol gateway allows routers operating inaccordance with one protocol to obtain and maintain certificates for aVPN from a certificate authority operating in accordance with anotherprotocol.

[0008] According to one aspect, the VPN enrollment protocol gateway isimplemented as a registration authority that operates as an intermediarybetween the router and the certificate authority. As a registrationauthority, the gateway is trusted by the certificate authority. Therouter communicates with the registration authority as if it were thecertificate authority, not realizing that it is communicating with anintermediary.

[0009] According to another aspect, the protocol gateway receives arouter enrollment request from the router. The protocol gateway decryptsthe request, adds an alterative subject name to the request, digitallysigns the request, and forwards the signed request to the certificateauthority. The certificate authority determines whether to trust thesource of the request (the protocol gateway), and proceeds to respondwith the requested certificate if it verifies that the gateway can betrusted. The gateway receives the requested certificate, encrypts anddigitally signs a response including the certificate, and returns thesigned and encrypted response to the router.

[0010] According to another aspect, the certificate authority may not beable to immediately issue a certificate, in which case it issues apending response. The registration authority maintains a mapping of arouter transaction ID (identifier) received from the router and apending response ID received from the certificate authority. Thismapping allows subsequent requests from the router with the sametransaction ID (e.g., querying whether the certificate has been issuedyet) to be properly matched to a request previously submitted to thecertificate authority for which a pending response was issued. Theregistration authority also maintains a mapping of a hash value of therequest received from the router to the pending response for thatrequest. This mapping allows the registration authority to determinewhen a request is resubmitted by the router (e.g., in the event therouter never receives a pending response returned to it by theregistration authority).

[0011] According to another aspect, the protocol gateway receives a getcertificate revocation list from the router. The protocol gatewaydecrypts the request and extracts from the request the certificateserial number of the signing certificate of the request. The protocolgateway then submits a Get Certificate by Serial Number request to thecertificate authority, which returns to the protocol gateway thecertificate corresponding to the serial number. The protocol gatewayextracts a certificate revocation list distribution point from theresponse, and obtains the certificate revocation list from thedistribution point. The protocol gateway then generates a responseincluding the certificate revocation list, encrypts and signs theresponse, and returns the response to the router.

[0012] According to another aspect, the protocol gateway receives a getcertificate request from the router. The protocol gateway decrypts therequest and extracts from the request the certificate serial number ofthe signing certificate of the request. The protocol gateway thensubmits a Get Certificate by Serial Number request to the certificateauthority, which returns to the protocol gateway the certificatecorresponding to the serial number. The protocol gateway then encryptsand signs a response including the certificate, and returns the responseto the router.

[0013] According to another aspect, the protocol gateway receives a getcertificate authority certificate request from the router. The protocolgateway generates a response message including the signing certificateof the registration authority as well as the encryption certificate ofthe registration authority, and returns the response message to therouter.

[0014] According to another aspect, the protocol gateway maintains arecord of passwords handed out to a router. A router obtains a passwordby communicating with the protocol gateway (or another device trusted bythe protocol gateway) via an authenticatable mechanism (e.g., SSL(Secure Sockets Layer)). A password is returned to the router, which canthen use this password for a request submitted to the protocol gateway.If the password presented by the router is in the router's record, thenthe request is processed; otherwise, the request is rejected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings. The same numbersare used throughout the figures to reference like components and/orfeatures.

[0016]FIG. 1 shows a virtual private network environment with anenrollment protocol gateway in accordance with certain embodiments ofthe invention.

[0017]FIG. 2 shows a general example of a computer that can be used inaccordance with certain embodiments of the invention.

[0018]FIG. 3 is a block diagram illustrating a registration authorityoperating as a protocol gateway between a router and a certificateauthority in accordance with certain embodiments of the invention.

[0019]FIG. 4 shows an exemplary transaction ID table in accordance withcertain embodiments of the invention.

[0020]FIG. 5 shows an exemplary request hash table in accordance withcertain embodiments of the invention.

[0021]FIG. 6 shows an exemplary password table in accordance withcertain embodiments of the invention.

[0022]FIGS. 7a and 7 b are a flowchart illustrating an exemplary processfor handling a router enrollment request in accordance with certainembodiments of the invention.

[0023]FIG. 8 is a flowchart illustrating an exemplary process forhandling pending responses in accordance with certain embodiments of theinvention.

[0024]FIG. 9 is a flowchart illustrating an exemplary process forhandling a Get Certificate Revocation List request in accordance withcertain embodiments of the invention.

[0025]FIG. 10 is a flowchart illustrating an exemplary process forhandling a Get Certificate request in accordance with certainembodiments of the invention.

[0026]FIG. 11 is a flowchart illustrating an exemplary process forhandling a Get Certificate Authority Certificate request in accordancewith certain embodiments of the invention.

[0027]FIG. 12 is a flowchart illustrating an exemplary process fordistributing and verifying passwords in accordance with certainembodiments of the invention.

DETAILED DESCRIPTION

[0028] The discussion herein assumes that the reader is familiar withcryptography. For a basic introduction of cryptography, the reader isdirected to a text written by Bruce Schneier and entitled “AppliedCryptography: Protocols, Algorithms, and Source Code in C,” published byJohn Wiley & Sons with copyright 1994 (or second edition with copyright1996).

[0029] In the discussion below, embodiments of the invention will bedescribed in the general context of computer-executable instructions,such as program modules, being executed by one or more conventionalpersonal computers. Generally, program modules include routines,programs, objects, components, data structures, etc. that performparticular tasks or implement particular abstract data types. Moreover,those skilled in the art will appreciate that various embodiments of theinvention may be practiced with other computer system configurations,including hand-held devices, multiprocessor systems,microprocessor-based or programmable consumer electronics, network PCs,minicomputers, mainframe computers, and the like. In a distributedcomputer environment, program modules may be located in both local andremote memory storage devices.

[0030] Alternatively, embodiments of the invention can be implemented inhardware or a combination of hardware, software, and/or firmware. Forexample, all or part of the invention can be implemented in one or moreapplication specific integrated circuits (ASICs).

[0031]FIG. 1 shows a virtual private network environment with anenrollment protocol gateway in accordance with certain embodiments ofthe invention. Generally, one or more client computers 102 cancommunicate with one or more server computers 104 via a public networksupporting a conventional virtual private network (VPN) 106. Servercomputers 104 can be coupled directly to the network supporting VPN 106,or alternatively can be coupled to the network supporting VPN 106 viaanother network, such as local area network (LAN) 108.

[0032] VPN 106 includes one or more routers 110, 112, and 114 throughwhich data is passed between client 102 and server 104. Routers 110-114are part of a public network, such as the Internet. Routers that arepart of other types of networks may also be included in VPN 106, such asrouters from a LAN or a private wide-area network.

[0033] Additionally, other networks may be involved in the communicationbetween client 102 and server 104. By way of example, client 102 mayconnect to the public network supporting VPN 106 via a conventionalmodem and a Public Switched Telephone Network (PSTN), via a conventionalcable modem and cable lines, etc.

[0034] Routers 110-114 can communicate with one another, as well asregistration authority 118, via any of a wide variety of conventionalcommunications protocols. In one implementation, routers 110-114communicate with one another and registration authority 118 using theHypertext Transfer Protocol (HTTP).

[0035] Each of the routers 110-114 receives data from one of the otherrouters 110-114 or alternatively from another component (e.g., a publicnetwork access provider, such as an Internet Service Provider (ISP);client computer 102; etc.). The data is then securely passed on toanother of the routers 110-114 or other components.

[0036] In order for data to be transmitted among routers 110-114, acertificate-based authentication scheme is employed. In such anauthentication scheme, each router 110-114 is assigned a uniquecertificate that it can use to authenticate itself to other routers orother computing devices (e.g., an ISP, a bridge or gateway, etc.).Additionally, these other computing devices may be part of VPN 106 andmay similarly be assigned unique certificates that can be used forauthentication. Such certificates can also optionally be used to encryptmessages between routers and/or other computing devices in any of avariety of conventional manners. For ease of explanation, routers aredescribed as the devices that are obtaining and maintaining certificatesfor VPN 106. The establishment and operation of a VPN is well-known tothose skilled in the art, and thus will not be discussed further exceptas it pertains to the invention.

[0037] The certificates used by routers 110-114 are assigned by atrusted certificate authority (CA) 116. The process of obtaining such acertificate is referred to as “enrollment”. In the illustrated example,routers 110-114 use a different enrollment protocol than is used bycertificate authority 116. A registration authority 118 communicateswith both routers 110-114 and certificate authority 116 and acts as anintermediary for enrollment, translating requests and responses in oneprotocol to another, as discussed in more detail below.

[0038]FIG. 2 shows a general example of a computer 142 that can be usedin accordance with certain embodiments of the invention. Computer 142 isshown as an example of a computer that can perform the functions of aclient computer 102, a server computer 104, a certificate authority 116,or a registration authority 118 of FIG. 1. Computer 142 includes one ormore processors or processing units 144, a system memory 146, and a bus148 that couples various system components including the system memory146 to processors 144.

[0039] The bus 148 represents one or more of any of several types of busstructures, including a memory bus or memory controller, a peripheralbus, an accelerated graphics port, and a processor or local bus usingany of a variety of bus architectures. The system memory includes readonly memory (ROM) 150 and random access memory (RAM) 152. A basicinput/output system (BIOS) 154, containing the basic routines that helpto transfer information between elements within computer 142, such asduring start-up, is stored in ROM 150. Computer 142 further includes ahard disk drive 156 for reading from and writing to a hard disk, notshown, connected to bus 148 via a hard disk driver interface 157 (e.g.,a SCSI, ATA, or other type of interface); a magnetic disk drive 158 forreading from and writing to a removable magnetic disk 160, connected tobus 148 via a magnetic disk drive interface 161; and an optical diskdrive 162 for reading from or writing to a removable optical disk 164such as a CD ROM, DVD, or other optical media, connected to bus 148 viaan optical drive interface 165. The drives and their associatedcomputer-readable media provide nonvolatile storage of computer readableinstructions, data structures, program modules and other data forcomputer 142. Although the exemplary environment described hereinemploys a hard disk, a removable magnetic disk 160 and a removableoptical disk 164, it 11 should be appreciated by those skilled in theart that other types of computer readable media which can store datathat is accessible by a computer, such as magnetic cassettes, flashmemory cards, digital video disks, random access memories (RAMs) readonly memories (ROM), and the like, may also be used in the exemplaryoperating environment.

[0040] A number of program modules may be stored on the hard disk,magnetic disk 160, optical disk 164, ROM 150, or RAM 152, including anoperating system 170, one or more application programs 172, otherprogram modules 174, and program data 176. Operating system 170 can beany of a variety of operating systems, such as any of the “Windows”family of operating systems available from Microsoft Corporation ofRedmond, Wash. A user may enter commands and information into computer142 through input devices such as keyboard 178 and pointing device 180.Other input devices (not shown) may include a microphone, joystick, gamepad, satellite dish, scanner, or the like. These and other input devicesare connected to the processing unit 144 through an interface 168 (e.g.,a serial port interface) that is coupled to the system bus. A monitor184 or other type of display device is also connected to the system bus148 via an interface, such as a video adapter 186. In addition to themonitor, personal computers typically include other peripheral outputdevices (not shown) such as speakers and printers.

[0041] Computer 142 can operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer188. The remote computer 188 may be another personal computer, a server,a router, a network PC, a peer device or other common network node, andtypically includes many or all of the elements described above relativeto computer 142, although only a memory storage device 190 has beenillustrated in FIG. 2. The logical connections depicted in FIG. 2include a local area network (LAN) 192 and a wide area network (WAN)194. Such networking environments are commonplace in offices,enterprise-wide computer networks, intranets, and the Internet. In thedescribed embodiment of the invention, remote computer 188 executes anInternet Web browser program such as the “Internet Explorer” Web browsermanufactured and distributed by Microsoft Corporation of Redmond, Wash.

[0042] When used in a LAN networking environment, computer 142 isconnected to the local network 192 through a network interface oradapter 196. When used in a WAN networking environment, computer 142typically includes a modem 198 or other means for establishingcommunications over the wide area network 194, such as the Internet. Themodem 198, which may be internal or external, is connected to the systembus 148 via a serial port interface 168. In a networked environment,program modules depicted relative to the personal computer 142, orportions thereof, may be stored in the remote memory storage device. Itwill be appreciated that the network connections shown are exemplary andother means of establishing a communications link between the computersmay be used.

[0043] Generally, the data processors of computer 142 are programmed bymeans of instructions stored at different times in the variouscomputer-readable storage media of the computer. Programs and operatingsystems are typically distributed, for example, on floppy disks orCD-ROMs. From there, they are installed or loaded into the secondarymemory of a computer. At execution, they are loaded at least partiallyinto the computer's primary electronic memory. The invention describedherein includes these and other various types of computer-readablestorage media when such media contain instructions or programs forimplementing the steps described below in conjunction with amicroprocessor or other data processor. The invention also includes thecomputer itself when programmed according to the methods and techniquesdescribed below. Furthermore, certain sub-components of the computer maybe programmed to perform the functions and steps described herein. Theinvention includes such sub-components when they are programmed asdescribed. In addition, the invention described herein includes datastructures, described herein, as embodied on various types of memorymedia.

[0044] For purposes of illustration, programs and other executableprogram components such as the operating system are illustrated hereinas discrete blocks, although it is recognized that such programs andcomponents reside at various times in different storage components ofthe computer, and are executed by the data processor(s) of the computer.

[0045]FIG. 3 is a block diagram illustrating an exemplary registrationauthority 118 operating as a protocol gateway between a router 210 and acertificate authority 116. Router 210 can be, for example, any ofrouters 110-114 of FIG. 1. Router 210 is configured (e.g., during aninstallation or setup process) with the address of registrationauthority 118 rather than CA 116 as the certificate authority. In theillustrated example, router 210 has no other knowledge that it iscommunicating with registration authority 118 rather than certificateauthority 116.

[0046] Communication between registration authority 118 and each ofrouter 210 and certificate authority 116 can be carried out using any ofa wide variety of conventional encryption and/or digital signingtechniques. By way of example, using well-known public key cryptographytechniques, a device obtains a private 11 key/public key pair; thepublic key is made available to other devices while the private key iskept secret by the device. Another device can encrypt a message intendedfor this device by using a conventional encryption algorithm and thisdevice's public key. The private key/public key pair and the encryptionalgorithm are chosen such that it is relatively easy to decrypt themessage with the private key, but extremely difficult to decrypt themessage without the private key. Similarly, a message can be digitallysigned by the device using a conventional encryption algorithm and itsprivate key. The digitally signed message can be decrypted by anotherdevice using the public key, allowing the other device to verify thatthe message came from that device. Alternatively, rather than applyingan encryption algorithm to the message itself, the encryption algorithmmay be applied to a hash value generated based on the message and aknown hash function. Different public key/private key pairs can be usedfor encryption and digital signatures, or alternatively the same publickey/private key pair can be used for both encryption and digitalsignatures.

[0047] Registration authority 118 operates as an enrollment agent forcertificate authority 116, allowing routers such as router 210 to enrollfor a VPN certificate from certificate authority 116 via registrationauthority 118. Registration authority 118 obtains, from certificateauthority 116, an enrollment agency signature certificate (e.g., byenrolling for an “Offline IPSec” enrollment agent signature certificate)and an encryption certificate (e.g., by enrolling for an “IPSecEncryption” certificate). In the illustrated examples, thesecertificates are used by registration authority 118 to digitally signdata sent to both the router 210 and the certificate authority 116, andto encrypt data sent to the router 210.

[0048] Router 210 communicates requests 212 to registration authority118 in accordance with the protocol supported by router 210. In theillustrated example, router 210 supports the protocol SCEP. Differenttypes of requests 212 can be transmitted to registration authority 118.In one implementation, registration authority 118 operates as a protocolgateway for the following types of requests: router enrollment, getcertificate revocation list (CRL), get certificate, get certificateauthority (CA) certificate, and password registration. The specificmanner in which each of these requests is handled by registrationauthority 118 is discussed in more detail below.

[0049] Upon receipt of an SCEP request 212, registration authority 118converts the request into an appropriate format for certificateauthority 116. The converted request is then digitally signed byregistration authority 118 and the signed request 214 is transmitted tocertificate authority 116. Certificate authority 116, receiving arequest in its own protocol (using PKCS #7 and PKCS #10), responds tothe request and issues a CA response 216. Registration authority 118receives the response 216, converts the response to the appropriate SCEPformat for router 210, and transmits an SCEP response 218 to router 210.Alternatively, for some requests registration authority 118 may generatethe response 218 without forwarding a signed request 214 to certificateauthority 116.

[0050] Registration authority 118 includes a protocol converter 220.Protocol converter 220 receives messages from router 210 and convertsthem as necessary to the proper protocol for certificate authority 116,and similarly receives messages from certificate authority 116 andconverts them to the proper protocol for router 210. The manner in whichprotocol converter 220 operates is dependent on the particular protocolsbeing used by router 210 and certificate authority 116.

[0051] In one implementation, registration authority 118 operates inaccordance with the Internet X.509 Public Key Infrastructure Certificateand CRL Profile (Network Working Group Request for Comments 2459,January 1999). Alternatively, other implementations may operate inaccordance with other standards.

[0052] Registration authority 118 also includes a transaction ID table222, a request hash table 224, and a password table 226. Tables 222-226are used by registration authority 118 to maintain information regardingrequests 212 and responses 216 in order to conform with the protocols ofrouter 210 and certificate authority 116.

[0053]FIG. 4 shows an exemplary transaction ID table in accordance withcertain embodiments of the invention. Transaction ID table 222 maintainsa mapping of router transaction IDs 228 to CA request IDs 230. A routertransaction ID 228 is received by registration authority 118 from router210 as part of each router enrollment message. Similarly, whencertificate authority 116 returns a pending response to registrationauthority 118, the pending response includes a CA request ID 230 (alsoreferred to as a “token”). Transaction ID table 222 allows registrationauthority 118 to query certificate authority 116 for the correctcertificate in response to subsequent requests from router 210 for thecertificate the pending response was issued for, as discussed in moredetail below.

[0054] Each entry in transaction ID table 222 is removed from table 222after a period of time. In one implementation, each entry in table 222is kept in table 222 for one week and then removed. This period of timecan optionally be configurable by a user or administrator.

[0055]FIG. 5 shows an exemplary request hash table in accordance withcertain embodiments of the invention. Request hash table 224 maintains amapping of certificate authority request IDs 232 to hash values of therequests 234. The hash value of a request is generated using any of avariety of conventional hashing functions, such as MD5 (Message Digest5). A hash function is a mathematical function that, given input data(e.g., the request) generates a unique output hash value based on theinput data. Thus, the hash value uniquely identifies a request butrequires less storage space than maintaining all of the request.Alternatively, table 224 could maintain the actual request rather thanhash values of the request.

[0056] Request hash table 224 allows registration authority 118 to“remember” router requests. For example, a pending response may beissued by registration authority 118 to router 210, as discussed in moredetail below. If a failure or problem occurs during the transmission(e.g., a network failure), then the pending response may not be receivedby router 210. If router 210 never receives the response, router 210will re-issue the same request. By maintaining table 224, registrationauthority 118 can determine when a received request is a re-issuedrequest, and need not submit another request for another new certificateto certificate authority 116.

[0057] Each entry in request hash table 224 is removed from table 224after a period of time. In one implementation, each entry in table 224is kept in table 224 for twenty minutes and then removed. This period oftime can optionally be configurable by a user or administrator.

[0058]FIG. 6 shows an exemplary password table in accordance withcertain embodiments of the invention. Password table 226 maintainspasswords 236 that are issued to router 210 in a secure manner. Suchpasswords can subsequently be used by router 210 to obtain acertificate, providing verification of the identity of router 210.

[0059] Each password in password table 226 is removed from table 226after a period of time. In one implementation, each password in table226 is kept in table 226 for sixty minutes and then removed. This periodof time can optionally be configurable by an administrator.

[0060] Returning to FIG. 3, in the illustrated example registrationauthority 118 is a dynamically linked library (DLL) referred to as the“MSCEP” DLL. Alternatively, registration authority 118 may include a DLLreferred to as the “MSCEP” DLL. Registration authority 118 includes aresponse module 238 that generates responses for certain requests fromrouter 210 that do not require forwarding to certificate authority 116.The operation of response module 238 is discussed in more detail below.

[0061] Registration authority 118 further hosts a web site 240.Alternatively, registration authority 118 may have a securecommunication link to a server hosting web site 240, thereby allowingdata to be securely passed between the server and registration authority118, or registration authority 118 may be software and/or firmware beingexecuted by a server that also hosts web site 240. Web site 240 allowspasswords to be securely issued to router 210 and stored in passwordtable 226, as discussed in more detail below.

[0062] Router Enrollment Request

[0063]FIGS. 7a and 7 b are a flowchart illustrating an exemplary processfor handling a router enrollment request in accordance with certainembodiments of the invention. Acts on the left-hand side of FIGS. 7a and7 b are implemented by registration authority 118 of FIG. 3, while actson the right-hand side are implemented by certificate authority 116. Theprocess of FIGS. 7a and 7 b may be performed in software, firmware,hardware, or a combination thereof. FIGS. 7a and 7 b are described withadditional reference to components in FIG. 3.

[0064] To participate in a VPN, router 210 enrolls for a certificatefrom certificate authority 116. Router 210 enrolls for a certificate bysending, as SCEP request 212, a router enrollment message (e.g., a SCEPPKCSReq message) to registration authority 118. The router enrollmentmessage includes a certificate enrollment request in accordance with thePublic-Key Cryptography Standards (PKCS) #10 standard. The certificateenrollment request is further encrypted (e.g., using the public key ofregistration authority 118) and then digitally signed by router 210 inaccordance with the Public-Key Cryptography Standards (PKCS) #7standard. Additional information regarding PKCS #7 and PKCS #10 isavailable from RSA Data Security, Inc. of Bedford, Mass. It should benoted that, although requests from router 210 use PKCS #7 and PKCS #10,certain information needed by certificate authority 116 is not includedin the requests. Registration authority 118 resolves this problem,adding information when necessary.

[0065] Registration authority 118 receives, as the router enrollmentmessage, this encrypted and digitally signed request (act 242). Uponreceipt of the enrollment message, registration authority 118 verifiesthe signature of the router enrollment message (act 244). If thesignature is not verified then the message is ignored (act 246).Alternatively, an indication of failure could be returned to router 210.

[0066] If the signature is verified, then registration authority 118decrypts the router enrollment message (e.g., using the private key ofregistration authority 118) and extracts the certificate enrollmentrequest from the message (act 248). Registration authority 118 uses thecertificate enrollment request to generate a request to the CA for anenrollment certificate in a format expected by certificate authority 116(act 250).

[0067] Router 210 needs a certificate with a subject alternative namesextension (SubjectAltName). However, router 210 does not specificallyrequest the SubjectAltName extension, and certificate authority 116 doesnot automatically add the extension. Registration authority 118 resolvesthis issue by adding, to the message it transmits to certificateauthority 116, the SubjectAltName extension in the request.

[0068] The PKCS #7 message, including both the subject alternative namesextension and the certificate enrollment request extracted from therouter enrollment message, is digitally signed by registration authority118 (act 252). This signed message is then transmitted to certificateauthority 116 as a CA request (act 254). Note that the CA request thusincludes a PKCS #7 message that is signed by registration authority 118,which in turn includes a certificate enrollment request that is signedby router 210.

[0069] Certificate authority 116 receives the CA request fromregistration authority 118 (act 256) and determines, based on thecontent of the CA request, whether to issue the requested certificate(act 258). The manner in which certificate authority 116 determineswhether to issue the requested certificate can vary. In oneimplementation, certificate authority 116 determines whether to issue acertificate based on whether the certificate of the registrationauthority 118 can be validated up to a trusted valid root and whetherthe certificate of registration authority 118 includes an extended keyusage indicating that registration authority 118 can be a registrationauthority (and thus operate as an enrollment agent). If both of theseconditions are satisfied, then a certificate is issued. Otherwise, thecertificate is not issued. Additionally, certificate authority 116 mayrequire that the certificate of registration authority 118 have beenissued directly by a certificate authority (that is, no intermediatecertificates in the chain from the registration authority certificate tothe certificate authority certificate).

[0070] If certificate authority 116 determines it will not issue acertificate, then certificate authority 116 generates a CA responseindicating failure (act 260). However, if certificate authority 116determines it will issue a certificate, then certificate authority 116generates the requested certificate (act 262) and then generates a CAresponse including the generated certificate (act 264).

[0071] The CA response generated by certificate authority 116 has nomessage content and is referred to as a “degenerated PKCS #7”. The PKCS#7 message, however, allows multiple certificates to be included in adegenerated PKCS #7 message. Certificate authority 116 returns the newlygenerated certificate as part of the degenerated PKCS #7 message.Additionally, the entire certificate chain from the generatedcertificate up to a root certificate may optionally be included in thedegenerated PKCS #7 message.

[0072] Certificate authority 116 then transmits the CA response(indicating either failure or with the generated certificate) toregistration authority 118 (act 266). Registration authority 118receives the CA response (act 268) and checks whether the CA responseincludes a certificate (act 270). If no certificate is included, thenregistration authority 118 generates an SCEP response message indicatingfailure (act 272). However, if such a certificate is included, thenregistration authority 118 extracts the certificate (act 274) andgenerates an SCEP response including the certificate (act 276). In theillustrated example, registration authority 118 extracts only thecertificate generated by certificate authority 116; the additionalcertificate chain (if included) is not used by registration authority118. Alternatively, the entire certificate chain could be included ifrouter 210 desired (or at least could handle) the chain.

[0073] Registration authority 118 then encrypts the SCEP response (act278) and digitally signs the encrypted response (act 280). The encryptedand signed response is then transmitted to router 210 (act 282), whichin turn can verify the signature and decrypt the response to extract thecertificate generated by certificate authority 116.

[0074] Pending Response Handling

[0075] In some situations, certificate authority 116 may not immediatelyissue a CA response with either a certificate or an indication that nocertificate will be issued. For example, certificate authority 116 maywait for an administrator to approve the issuing of the certificate. Insuch situations, certificate authority 116 issues a CA pending responsefrom certificate authority 116.

[0076]FIG. 8 is a flowchart illustrating an exemplary process forhandling pending responses in accordance with certain embodiments of theinvention. The process of FIG. 8 is implemented by registrationauthority 118 of FIG. 3, and may be performed in software, firmware,hardware, or a combination thereof. FIG. 8 is described with additionalreference to components in FIGS. 3-7b.

[0077] Registration authority 118 receives the CA pending response fromcertificate authority 116 (act 302). Upon receipt of the CA pendingresponse, registration authority 118 adds entries to its transaction IDtable 222 (act 304) and its request hash table 224 (act 306).Registration authority 118 also generates an encrypted and digitallysigned SCEP pending response message (act 308) and transmits theencrypted and signed message to router 210 (act 310).

[0078] Typically, in response to an SCEP pending response message,router 210 will re-issue its request for a certificate (e.g., via aGetCertInitial message). Registration authority 118 waits until itreceives an additional SCEP request for the certificate from the router210 (act 312). Once the additional request is received, registrationauthority 118 accesses transaction ID table 222 to determine theappropriate CA request ID (act 314). Registration authority 118 uses theCA request ID from table 222 to generate a CA request for a certificatecorresponding to the CA request ID and digitally signs the CA request(act 316). The signed CA request is then transmitted to certificateauthority 116 (act 318).

[0079] Upon receiving the CA request, certificate authority 116 mayissue another pending response to registration authority 118 oralternatively determine whether to issue the certificate (per act 258 ofFIG. 7a discussed above). Upon receipt of a response from certificateauthority 116, registration authority 118 determines whether theresponse is another pending response (act 320). If the response isanother pending response, the registration authority 118 returns to act308 and generates and encrypted and signed SCEP pending responsemessage. However, if the response is not another pending response, thenregistration authority 118 proceeds per acts 268-282 of FIG. 7b toreturn an appropriate response to router 210.

[0080] Use of request hash table 224 further allows registrationauthority 118 to gracefully recover in the event the SCEP pendingresponse message is not received by router 210. If router 210 does notreceive the pending response message, then it will resubmit its originalrequest (e.g., an SCEP PKCSReq message). In order to avoid a duplicaterequest to certificate authority for the certificate, registrationauthority 118 generates the hash value for SCEP PKCSReq messages itreceives and compares the hash value to the entries in request hashtable 224. If the hash value matches an entry, then registrationauthority 118 uses the CA request ID from table 224 to generate a CArequest for a certificate corresponding to the CA request ID (act 316),rather than generating a CA request including a certificate enrollmentrequest (act 250 of FIG. 7a). Processing then continues as discussedabove with reference to FIG. 8.

[0081] Get Certificate Revocation List Request

[0082] Returning to FIG. 3, router 210 may also send a Get CertificateRevocation List (CRL) request as SCEP request 212. The requestidentifies a serial number or similar identifier of a certificate forwhich the corresponding CRL should be retrieved. The CRL is a listidentifying revoked certificates which is made available by thecertificate authority (typically in a public repository). The CRL can bechecked to determine whether a particular serial number (typicallyidentified in the CRL by its serial number) has been revoked.Registration authority 118 responds to such a request by obtaining therequested CRL and returning it to router 210.

[0083]FIG. 9 is a flowchart illustrating an exemplary process forhandling a Get Certificate Revocation List request in accordance withcertain embodiments of the invention. The process of FIG. 9 isimplemented by registration authority 118 of FIG. 3, and may beperformed in software, firmware, hardware, or a combination thereof.FIG. 9 is described with additional reference to components in FIG. 3.

[0084] Initially, registration authority 118 receives the Get CRLrequest (e.g., an SCEP GetCRL message) from router 210 (act 330).Registration authority 118 decrypts the request (act 332), verifies thesignature of the decrypted request (act 334), and proceeds based onwhether the signature is verified (act 336). If the signature cannot besuccessfully verified, then the message is dropped (act 338);registration authority 118 simply ignores the message. Alternatively,registration authority 118 may return an indication to router 210 thatthe signature could not be verified.

[0085] However, if the signature is successfully verified, thenregistration authority 118 extracts the certificate serial number fromthe decrypted request (act 340). This serial number can be extracted byobtaining the serial number of the certificate used by router 210 tosign the Get CRL request.

[0086] Registration authority 118 then uses the extracted serial numberto generate a Get Certificate by Serial Number request (act 342). TheGet Certificate by Serial Number request is then digitally signed andtransmitted to certificate authority 116 (act 344), which in turnaccesses its records to identify the certificate corresponding to thegiven serial number. This certificate is then returned by certificateauthority 116 to registration authority 118 (act 346).

[0087] The certificate returned by certificate authority 116 includes aCRL distribution point, which is an identifier of a location (e.g., auniform resource locator (URL)) at which the CRL corresponding to thecertificate can be obtained. Upon receipt of the certificate,registration authority 118 extracts the CRL distribution point from thecertificate (act 348). Registration authority 118 then accesses (e.g.,via HTTP) the identified location and retrieves the CRL located there(act 350).

[0088] Upon obtaining the CRL, registration authority 118 generates anSCEP response message including the CRL (act 352). Registrationauthority 118 then encrypts and digitally signs the SCEP responsemessage including the CRL, and returns the encrypted and signed SCEPresponse message to router 210 (act 354).

[0089] Alternatively, the Get CRL request received from router 210 (act330) may include the certificate for which the corresponding CRL is tobe obtained. In this situation, the CRL distribution point can beextracted by accessing the included certificate, thereby alleviating theneed to access certificate authority 116 (acts 340-346).

[0090] Get Certificate Request

[0091] Returning to FIG. 3, router 210 may also send a Get Certificaterequest as SCEP request 212. The request identifies a serial number of acertificate that the router would like returned to it. Router 210 maymake such a request, for example, in situations where it has kept theserial number of a certificate it needs but has not kept the actualcertificate. Registration authority 118 responds to such a request byobtaining the requested certificate and returning it to router 210.

[0092]FIG. 10 is a flowchart illustrating an exemplary process forhandling a Get Certificate request in accordance with certainembodiments of the invention. The process of FIG. 10 is implemented byregistration authority 118 of FIG. 3, and may be performed in software,firmware, hardware, or a combination thereof. FIG. 10 is described withadditional reference to components in FIG. 3.

[0093] Initially, registration authority 118 receives the GetCertificate request (e.g., an SCEP GetCert message) from router 210 (act362). Registration authority 118 decrypts the request (act 364),verifies the signature of the decrypted request (act 366), and proceedsbased on whether the signature is verified (act 368). If the signaturecannot be successfully verified, then the message is dropped (act 370);registration authority 118 simply ignores the message. Alternatively,registration authority 118 may return an indication to router 210 thatthe signature could not be verified.

[0094] However, if the signature is successfully verified, thenregistration authority 118 extracts the certificate serial number fromthe decrypted request (act 372). This serial number can be extracted byobtaining the serial number specified in the request (e.g., as thecertificate serial number of the signing certificate of the request).

[0095] Registration authority 118 then uses the extracted serial numberto generate a Get Certificate by Serial Number request (act 374). TheGet Certificate by Serial Number request is then digitally signed andtransmitted to certificate authority 116 (act 376), which in turnaccesses its records to identify the certificate corresponding to thegiven serial number. This certificate is then returned by certificateauthority 116 to registration authority 118 (act 378).

[0096] Registration authority 118 then generates an SCEP responsemessage including the certificate received in act 378 (act 380).Registration authority 118 then encrypts and digitally signs the SCEPresponse message including the certificate, and returns the encryptedand signed SCEP response message to router 210 (act 382).

[0097] Get CA Request

[0098] Returning to FIG. 3, router 210 may also send a Get CA request asSCEP 11 request 212. The request is an HTTP Get call to a URL hosted byregistration authority 118. The URL is made available to router 210during setup or configuration of router 210. Registration authority 118responds to such a request by returning the requested certificates torouter 210.

[0099]FIG. 11 is a flowchart illustrating an exemplary process forhandling a Get Certificate Authority Certificate request in accordancewith certain embodiments of the invention. The process of FIG. 11 isimplemented by registration authority 118 of FIG. 3, and may beperformed in software, firmware, hardware, or a combination thereof.FIG. 11 is described with additional reference to components in FIG. 3.

[0100] Initially, a Get CA request is received by registration authority118 from router 210 (act 400). Upon receipt of the request, registrationauthority 118 obtains a DLL name identified by the request (act 402). Inone implementation, an exemplary Get CA request from router 210 is inthe following form:

[0101] GETmscep.dll/cgi-bin/pkiclient.exe?operation=GetCACert&message=<Base64encoded authority issuer identifier>

[0102] In this implementation, registration authority 118 is implementedas an IIS (Internet Information Server) ISAPI (Internet ServerApplication Programming Interface) DLL. Upon receipt of such a request,IIS parses the input through to identify the first DLL and attempts toload that DLL if necessary. Thus, the remainder of the request can beignored by registration authority 118 in determining how to respond tothe request.

[0103] Registration authority 118 is the identified DLL, which in theillustrated example is “mscep.dll”, and passes the request to responsemodule 238 (act 404). In response to being passed the message (either inits entirety, or a part thereof), response module 238 generates adegenerated PKCS #7 message including the signing certificate and theencryption certificate of registration authority 118 (act 406), andreturns the degenerated PKCS #7 message to the router (act 408). Thus,router 210 requests the certificates for the certificate authority, butreceives the certificates for the registration authority instead.

[0104] Alternatively, registration authority 118 may include acertificate chain in the message it generates in act 408. By way ofexample, MSCEP DLL 328 may send a certificate request to certificateauthority 116, which returns the certificate of certificate authority116 and a certificate chain that extends up to its root certificate.

[0105] Password Handling

[0106] Returning to FIG. 3, router 210 may also make use of a passwordto authenticate itself to certificate authority 116 (actuallyregistration authority 118, but router 210 is not aware of this). Thepassword allows registration authority 118 (and thus certificateauthority 116, which trusts registration authority 118) to know that aparticular request actually came from the router claiming to have sentit. The password may be used with one or more of the different types ofSCEP requests 212 discussed above. By way of example, the password maybe used with the router enrollment request.

[0107]FIG. 12 is a flowchart illustrating an exemplary process fordistributing and verifying passwords in accordance with certainembodiments of the invention. The process of FIG. 12 is implemented byregistration authority 118 of FIG. 3, and may be performed in software,firmware, hardware, or a combination thereof. FIG. 12 is described withadditional reference to components in FIG. 3.

[0108] Initially, registration authority 118 receives a request for apassword (act 430). This request is received via a mechanism that allowsregistration authority 118 to authenticate the requestor, such as by useof SSL (Secure Sockets Layer) to authenticate the requestor whenaccessing web site 240 of FIG. 3. The requestor could be a computerbeing operated by a router administrator, or alternatively router 210.Upon receipt of the request, registration authority 118 attempts toauthenticate the requester, such as the router administrator, (act 432)and proceeds based on whether the authentication is successful (act434). If the requestor cannot be authenticated, then the request for apassword is denied (act 436). The request may simply be ignored, oralternatively an indication may be returned to the requestor that therequest for a password is denied.

[0109] However, if the router is authenticated, then registrationauthority 118 proceeds to generate a password and add the newlygenerated password to password table 226 (act 438). The password can begenerated by registration authority 118 in any of a wide variety ofconventional manners, such as by generating a random (or pseudo-random)number and/or sequence of letters. The generated number may then beplaced into a particular format if needed by either router 210 orcertificate authority 116, such as hexadecimal format, binary codeddecimal format, etc.

[0110] The password added to password table 226 is removed from table226 after a period of time. In one implementation, each password intable 226 is kept in table 226 for sixty minutes and then removed. Thisperiod of time can optionally be configurable by an administrator.

[0111] Registration authority 118 then returns the newly generatedpassword to requestor (act 440). This return of the password is done ina secure manner, such as by use of SSL.

[0112] Eventually, registration authority 1118 receives a request fromrouter 210 that includes a password that needs to be verified (act 442).Upon receipt of such a request, registration authority 1118 determineswhether the received password is in password table 226 (act 444). If thereceived password is not in password table 226, then the request isrejected (act 446). The request can simply be ignored, or alternativelya rejection response can be returned to router 210 (e.g., informingrouter 210 that the password it provided was not valid).

[0113] However, if the password is in password table 226, then therequest is processed by registration authority 1118 (act 448).Registration authority 1118 may also optionally remove the password frompassword table 226 (act 450), thereby adding an additional level ofsecurity by allowing each password to be used only once.

CONCLUSION

[0114] Thus, a VPN enrollment protocol gateway has been described. Theprotocol gateway is implemented as a registration authority that istrusted by the certificate authority, and operates as an intermediarybetween the router and the certificate authority. The protocol gatewayadvantageously allows routers operating in accordance with one protocolto obtain and maintain certificates for a VPN from a certificateauthority operating in accordance with another protocol.

[0115] Although the description above uses language that is specific tostructural features and/or methodological acts, it is to be understoodthat the invention defined in the appended claims is not limited to thespecific features or acts described. Rather, the specific features andacts are disclosed as exemplary forms of implementing the invention.

1. A method comprising: receiving a request, from a requester, for a password to be used by a device when communicating with a registration authority; authenticating the requestor; generating the password; adding the password to a password table; and returning the password to the requestor for use by the device.
 2. A method as recited in claim 1, wherein the device comprises a router.
 3. A method as recited in claim 1, wherein generating the password comprises generating a random number as the password.
 4. A method as recited in claim 1, wherein receiving, authenticating, and returning include using Secure Sockets Layer (SSL) to maintain secure communication with the device.
 5. A method as recited in claim 1, further comprising keeping the password active for a selected amount of time.
 6. A method as recited in claim 5, wherein keeping the password active for a selected amount of time comprises marking the password as invalid after the selected amount of time.
 7. A method as recited in claim 5, wherein keeping the password active for a selected amount of time comprises removing the password from the password table after the selected amount of time.
 8. A method as recited in claim 1, further comprising: receiving a request from the device, the request including a request password; checking whether the request password is included in the password table; and processing the request if the request password is included in the password table, otherwise rejecting the request.
 9. A method as recited in claim 8, further comprising removing, if the request password is included in the password table, the request password from the password table.
 10. One or more computer-readable media having stored thereon a plurality of instructions that, when executed by one or more processors, causes the one or more processors to perform acts comprising: receiving a request, from a requester, for a password to be used by a device when communicating with a registration authority; authenticating the requestor; generating the password; adding the password to a password table; and returning the password to the requestor for use by the device.
 11. One or more computer-readable media as recited in claim 10, wherein the device comprises a router.
 12. One or more computer-readable media as recited in claim 10, wherein generating the password comprises generating a random number as the password.
 13. One or more computer-readable media as recited in claim 10, wherein receiving, authenticating, and returning include using Secure Sockets Layer (SSL) to maintain secure communication with the device.
 14. One or more computer-readable media as recited in claim 10, wherein the plurality of instructions further cause the one or more processors to perform acts comprising keeping the password active for a selected amount of time.
 15. One or more computer-readable media as recited in claim 14, wherein keeping the password active for a selected amount of time comprises marking the password as invalid after the selected amount of time.
 16. One or more computer-readable media as recited in claim 14, wherein keeping the password active for a selected amount of time comprises removing the password from the password table after the selected amount of time.
 17. One or more computer-readable media as recited in claim 10, wherein the plurality of instructions further cause the one or more processors to perform acts comprising: receiving a request from the device, the request including a request password; checking whether the request password is included in the password table; and processing the request if the request password is included in the password table, otherwise rejecting the request.
 18. One or more computer-readable media as recited in claim 17, wherein the plurality of instructions further cause the one or more processors to perform acts comprising removing, if the request password is included in the password table, the request password from the password table.
 19. A system comprising: means for receiving a request, from a requester, for a password to be used by a device when communicating with a registration authority; means for authenticating the requestor; means for generating the password; means for adding the password to a password table; and means for returning the password to the requestor for use by the device.
 20. A system as recited in claim 19, wherein the device comprises a router. 